The present invention relates to a method and an apparatus for ordering a working operation to workers in an assembling line, and more particularly to a method and an apparatus for ordering a working operation in an automobile assembling line in which parts different models are assembled.
In manufacturing parts such as automobiles, products for different models are sometimes manufactured in a common assembly line. For example, in an automobile body assembly line, different kinds of automobiles whose models and grades are determined by a production plan, are generally assembled in a common line. The production plan determines the number of automobiles to be manufactured, according to the consumers' orders. In such as assembly line, the working order which indicates the workers' job in a line, has generally been determined by two methods. The first method involves preparing a working order sheet by a production plan and distributing the working order sheet to workers. Workers determine kind of the automobile to be manufactured from the working order sheet. The second method involves memorizing the working order beforehand in a shift register, and the working order by an indicator as each automobile body is transferred.
However, according to the above-described first method, after workers confirm the transferred automobile bodies by the working order sheet, worders have to assemble a predetermined part onto an automobile or machine automobile bodies. Hence, it is troublesome for workers to confirm the transferred automobile bodies by the working order sheet. This also can be disadvantageous because workers can erroneously read the working order sheet, thereby manufacturing a defective automobile body which is different from the body designated on the working order sheet.
On the other hand, according to the above-described second method employing a shift register, a working order is indicated in every transferred automobile body, and workers assemble a predetermined part or machine a transferred automobile body according to the working operation instructed by the indicator. Hence, mistaken working operations are considerably reduced. However, the disadvantage of the production of automobile bodies, which are different from the body indicated by the indicator remains, because of the mistakes by workers or mistaken communication between the indicator and other devices. Mistakes by workers occurs when, for example, a worker presses a push button twice in a short time. In this case, the push button outputs only one shift pulse even when the push button is pressed twice. In the case that a shift pulse is issued in response to a transfer of an automobile body, the mistaken communication between devices occurs when a transfer machine, is not synchronized with the shift register, or when a relay switch generates a chattering. Based upon the workers' mistaken operation or the mistaken communication between devices, a working order which is different from the working order memorized in the shift register, is sometimes instructed by the indicator. For example, as shown in FIG. 5(A), when working order data is memorized in a shift register 10 in an order such as "a", "a", "b", "a", "b", and "b", the shift register 10 issues an indicator signal "IS" to an indication 12 in the order memorized in the shift register 10 upon the consecutive supply of the shift pulse "SP". That is, when the shift pulses SP.sub.1, SP.sub.2, . . . , SP.sub.5 are consecutively supplied into the shift register 10, as shown in FIG. 5(B), the shift register 10 outputs the indication signals into the indicator 12, which designates the data memorized in the shift register 10, "a", "a", . . . , and "b". The indicator 12 is designed to consecutively indicate the working order "a'", "a'", . . . , "b'" corresponding to the data "a", "a", . . . , "b", respectively. However, as shown in FIG. 5(C), if the shift pulses SP.sub.1 and SP.sub.2 are supplied into the shift register 10 in a short time for reasons such as a chattering at a relay switch, the shift register 10 consecutively outputs the indication signal "IS" corresponding to the data "a", but the indicator 12 cannot reply to the second shift pulse SP.sub.2 because of the short time interval between the first and second signals. Hence, when the next shift pulse SP.sub.3 is supplied to the indicator 12, the indicator 12 indicates the working order "b'" corresponding to the data "b". Thus, the data "a" memorized in the shift register 10 as the second order is not indicated by the indicator 12. As workers work according to the working order indicated by the indicator 12, workers have no doubt as to the indicated order even if a mistaken indication is indicated by the indicator 12. Hence, workers cannot easily find that the indication is mistaken, thereby causing delay in the discovery of the problem. Further, if an indication mistake is made once, defective products which are different from the predetermined body by one automobile are manufactured, thus causing a number of defective products.
The above-described second method is further explained in detail by an example of an assembly which assembles two kinds of automobile model bodies "a" and "b". In FIG. 6, sub-lines 14 and 16 are the lines which manufacture an engine compartment 18 and a front floor 20 for two models "a" and "b" as shown in FIG. 7. The manufactured engine compartment 18 and front floor 20 are combined at a station 22 as shown in FIG. 6, thereby forming an under front 24. Subsequently, final assembly is made in a final line 26. Working order instructing apparatuses 28 and 30, which include the shift registers 10 and the indicators 12 therein, are provided at the head portions of the sub-lines 14 and 16, respectively. The working order instructing apparatuses 28 and 30 instruct the model of automobiles to be manufactured in the sub-lines 14 and 16, respectively. The shift registers 10 of the working order instructing apparatuses 28 and 30 memorize the same data as those shown in FIG. 5(A), respectively. "a model of an automobile" and "b model of an automobile" are herein referred to as "a" and "b", hereunder respectively.
In the parallel sub-lines 14 and 16, engine compartments 18 and front floors 20, both of which are employed in the same model of automobile, are manufactured at the same time. The engine compartments 18 and front floors 20, manufactured in the sub-lines 14 and 16, are designed to be assembled at the station 22. If the mistaken indication as shown in FIG. 5(C) occurs, the sub-line 16 does not manufacture the front floor 20 for the "a" model automobile which is to be manufactured by the second order. Hence, the engine compartments 18 and front floors 20, which are subsequently manufactured in the sub-lines 14 and 16 respectively, do not coincide with those determined by the production plan. As a result, at the station 22, an engine compartment 18 for use of "a" model is assembled into a front floor 20 for use of "b" model, or an engine compartment 18 for use of "b" is assembled into a front floor for use of "a" model. Thus, many defective parts are manufactured.
Moreover, if the defective parts caused by the mistaken instruction of the working order instructing apparatuses or by the mistaken working operation, are discovered on the way assembly line, all that is known is that the defective assembly is different from the automobile model of the production plan. Hence, it is troublesome to identify the mistaken working operation or the mistaken assembled parts. Thus, a lot of time is required to solve the problems.